The goal of this project is to understand the role of oxygen- derived radicals on cardiac cell injury during ischemia and post- ischemic reperfusion. Mechanisms and characteristics of cell injury by hydrogen peroxide (H2O2), superoxide (O2) and hydroxyl (OH.) radicals exposure in myocyte cultures and intact myocardium will be investigated. In addition, in order to further investigate the cell injury, sites of O2 and OH. production in myocytes will be studied. A major focus of the current proposal is to understand the role hydrogen peroxide and hydroxyl radical play in the pathogenesis of ischemia mediated cardiac cell injury. We are proposing that (1) H2O2 is one of important O2 metabolites in causing injury to myocytes through OH. production and lipid peroxidation. Since the generation of H2O2 is closely linked with O2, the damage by individual metabolites in the cell injury is not known. We will concentrate our efforts on understanding the role H2O2 (alone or in combination with O2) plays in cell damage; (2) we will directly investigate the OH. production during post-ischemic reperfusion, correlate it with resultant injury quantitatively and study the intracellular mechanism leading to OH. formation from H2O2. We also propose to demonstrate that myocytes produce O2/OH. during post-anoxic reoxygenation, and this production is primarily linked to metabolic abnormalities and the reperfusion of mitochondrial respiration. Superoxide and OH. generated in both hearts and myocytes will be directly identified and measured by cytochrome C assay and high pressure liquid chromatography. The cell injury will be correlated with heart function, altered biochemistry and quantitative cell damage before and after therapeutic interventions. Experiments proposed utilizing isolated cultured myocytes will allow us to study the direct effect of specific oxygen radical species and the progressive stages in the process of cell death as will be visualized by microscopic markers. Direct knowledge of ischemic cell injury caused by specific oxygen-derived radicals will be important in the development of new improved palliative strategies to retard or prevent myocardial injury in man.